Conventional methods for manufacturing semiconductor devices comprise numerous processing steps, many of which involve the deposition of a metal by CVD and subsequently etching portions of the deposited metal to form a conductive pattern and/or interconnection. Typically, such CVD is conducted in an apparatus comprising a CVD chamber. A conventional processing sequence comprises preconditioning the chamber by introducing the metallic species to be deposited prior to actual deposition, CVD, and cleaning the chamber. During such processing, vapors are continuously removed from the CVD chamber by a vacuum pump through an effluent line. The effluent vapors, which include reaction products, are usually environmentally harmful. Accordingly, conventional practices also comprise employing a scrubber, such as a dry or wet scrubber, in communication with the effluent line for treatment of vapors removed from the chamber.
Severe clogging problems usually occur in such conventional CVD systems. One type of acute clogging problem occurs in the effluent line due to condensation of vapors resulting in the deposition of particulate material. Another clogging problem occurs proximate the inlet of a wet scrubber in the moisture-rich area, usually just above the water tip-over insert. For example, W is typically deposited during various phases of manufacturing a semiconductor device by CVD employing tungsten hexafluoride (WF.sub.6). A conventional apparatus employed for CVD comprises a CVD chamber in which preconditioning, CVD, and chamber cleaning are conducted. Chamber cleaning typically comprises removing tungsten as well as any reaction products from the internal walls of the chamber, and is conventionally conducted utilizing a fluorinated species such as SF.sub.6 /O.sub.2, NF.sub.3 /O.sub.2, CF.sub.4 /O.sub.2, C.sub.2 F.sub.6 or NF.sub.3. Vapors are removed from the CVD chamber by a vacuum pump through an effluent line in communication with a downstream wet scrubber. Clogging of the effluent line and clogging in proximity to the inlet of the wet scrubber have become serious problems which result in equipment downtime, product uniformity, and exposure to toxic wastes.
A conventional apparatus utilized in the manufacture of semiconductor devices for CVD is schematically illustrated in FIG. 1 and comprises a CVD chamber 10. Process generated vapors are removed from chamber 10 by vacuum pump 11 through effluent line 12. As shown by the path of arrows, the vapors removed from chamber 10 are passed via effluent line 12 to scrubber 14. When employing a dry scrubber, a filter 13 shown in FIG. 1, is conventionally employed to remove particulate material. When employing a wet scrubber, the depicted filter 13 is omitted. The effluent from the scrubber is exhausted through vent 15. Severe clogging usually occurs in effluent line 12, particularly at elbows, such as at 90.degree. elbow 16. In addition, clogging usually occurs near the inlet of a wet scrubber in the moisture-rich area.
A conventional wet scrubber, i.e., Vector ES-Series Fume Scrubber 20 marketed by ATMI ECOSYS Corp., of Santa Clara, Calif., is schematically illustrated in FIG. 2. The relevant portions of the depicted wet scrubber comprise water inlet 21, tip-over insert 22, lower O-ring seal of the throat 23, nitrogen ports 24, upper O-ring seal of the throat 25, lower band clamp 26, upper and lower spoolpiece O-rings 27 and upper band clamp 28. Clogging usually cccurs approximate the tip-over insert as at 29.
When depositing W by CVD in a conventional apparatus comprising a CVD chamber, particulate deposition and consequential clogging of effluent line 12 (FIG. 1), such as at elbow 16, is usually due to condensation of tungsten oxyfluoride WOF.sub.4, believed to be a by-product generated primarily during the chamber cleaning phase of a typical W-CVD process. WOF.sub.4 is a white crystalline solid with a melting point of 100.degree. C. and a boiling point of 185.degree. C. The vapor pressure of the solid is about 1 Torr at 56.degree. C.; and about 20 Torr at 100.degree. C. Due to its extremely low vapor pressure, WOF.sub.4 condenses out as a solid as the temperature decreases along the effluent line. Thus, in practice, effluent line 12 has been found coated with white dry WOF.sub.4 powder all the way from the pump outlet port to the inlet of the wet scrubber, resulting in severe clogging problems, particularly at elbows. It has been observed that as much as 95% of the particulate clogging problem is attributable to WOF.sub.4 powder.
In a conventional wet scrubber just above the water tip-over pipe, there is a moisture-rich area which creates a different clogging problem than that caused by condensation of WOF.sub.4 along effluent line 12. In the moisture-rich area of the wet scrubber, clogging occurs due to WO.sub.3 solids. It is believed that such WO.sub.3 solids result during chamber precoating and deposition steps, when a significant amount of unreacted gaseous WF.sub.6 is released into the effluent line. WF.sub.6 hydrolyzes in the presence of moisture to generate WO.sub.3 solids which are deposited in the moisture-rich area of the wet scrubber. In addition, during chamber cleaning, gaseous WOF.sub.4 in the exhaust system is usually hydrolyzed to form WO.sub.3 solids.
Prior attempts to address particulate clogging in an apparatus comprising a W-CVD chamber involve wrapping a heating blanket or electrical heating tape around the effluent line to maintain the exhaust stream at an elevated temperature above the condensation temperature of WOF.sub.4. This approach has not proved particularly affective, and frequent, time consuming, exhaust line cleaning is still required.
A prior attempt to address WO.sub.3 clogging in a wet scrubber of an apparatus comprising a W-CVD chamber involves spraying water to dissolve deposited WO.sub.3. This solution has also not been found particularly effective and is quite cumbersome.
Accordingly, there exists a need to prevent or substantially reduce clogging in an apparatus comprising a CVD chamber, particularly deposited WOF.sub.4 in the effluent line of an apparatus for W deposition by CVD. There also exists a need for a simplified, cost-effective manner to reduce and/or remove deposited particulate material in a wet scrubber downstream of and in communication with the effluent line, particularly deposited WO.sub.3.